Java 线程和jsoup错误：ava.lang.RuntimeException:执行doInBackground（）时出错

我正在研究jsoup库，并编写了以下简单代码来观察它是如何工作的： 我有以下代码，其中我尝试连接到google.com并解析该网站上的文本：

我的代码：

public class MainActivity extends Activity  {
    ProgressDialog _dialog;
    String title; 

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        _dialog = new ProgressDialog(this);
        _dialog.setMessage("Jsoup parsing...");
        StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
        StrictMode.setThreadPolicy(policy);
        new TheTask().execute();
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {

        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }
    class TheTask extends AsyncTask<Void,String,String>
    {

        @Override
        protected String doInBackground(Void... arg0) {
            // TODO Auto-generated method stub
               Document doc;                                      
                try {                                              
                    doc = Jsoup.connect("http://google.com/").get();
                    title = doc.title();  
                }
                catch(Exception e)
                {
                    e.printStackTrace();
                }
            return title;
        }

        @Override
        protected void onPostExecute(String result) {
            // TODO Auto-generated method stub
            super.onPostExecute(result);
            _dialog.dismiss();
        }

        @Override
        protected void onPreExecute() {
            // TODO Auto-generated method stub
            super.onPreExecute();
            _dialog.show();
        }

    }
}

---

原因：java.lang.NoClassDefFoundError:org.jsoup.jsoup如何解决问题？非常感谢@JunedAhsan。解决了的

    06-21 20:26:38.487: E/AndroidRuntime(1766): FATAL EXCEPTION: AsyncTask #1
06-21 20:26:38.487: E/AndroidRuntime(1766): Process: com.mmexample.newschanr, PID: 1766
06-21 20:26:38.487: E/AndroidRuntime(1766): java.lang.RuntimeException: An error occured while executing doInBackground()
06-21 20:26:38.487: E/AndroidRuntime(1766):     at android.os.AsyncTask$3.done(AsyncTask.java:300)
06-21 20:26:38.487: E/AndroidRuntime(1766):     at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:355)
06-21 20:26:38.487: E/AndroidRuntime(1766):     at java.util.concurrent.FutureTask.setException(FutureTask.java:222)
06-21 20:26:38.487: E/AndroidRuntime(1766):     at java.util.concurrent.FutureTask.run(FutureTask.java:242)
06-21 20:26:38.487: E/AndroidRuntime(1766):     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
06-21 20:26:38.487: E/AndroidRuntime(1766):     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
06-21 20:26:38.487: E/AndroidRuntime(1766):     at java.lang.Thread.run(Thread.java:841)
06-21 20:26:38.487: E/AndroidRuntime(1766): Caused by: java.lang.NoClassDefFoundError: org.jsoup.Jsoup
06-21 20:26:38.487: E/AndroidRuntime(1766):     at com.mmexample.newschanr.MainActivity$TheTask.doInBackground(MainActivity.java:74)
06-21 20:26:38.487: E/AndroidRuntime(1766):     at com.mmexample.newschanr.MainActivity$TheTask.doInBackground(MainActivity.java:1)
06-21 20:26:38.487: E/AndroidRuntime(1766):     at android.os.AsyncTask$2.call(AsyncTask.java:288)
06-21 20:26:38.487: E/AndroidRuntime(1766):     at java.util.concurrent.FutureTask.run(FutureTask.java:237)
06-21 20:26:38.487: E/AndroidRuntime(1766):     ... 3 more